1. Field of the Invention
This invention pertains to the general field of herbicides, to novel herbicidal compounds and intermediates thereto, as well as to compositions containing the active compounds, and to new methods for the control of undesired plant growth by preemergence or postemergence application of the novel active compounds and compositions.
2. Description of the Prior Art
It has long been man's desire to promote the growth of certain plant species, those species which serve as food for man or for his animals, species which protect him from the elements, such as trees and shrubbery, and species which he finds aesthetically attractive, such as flowers. Centuries ago man learned to promote the growth of plants by applying fertilizer to them. Great commercial enterprises have been built upon processes for producing ammonia, urea, phosphates, potash, and other materials incorporated into fertilizer compositions. The value in the use of fertilizer for promoting plant growth is well known.
Man has probably always realized that certain foreign plant species, weeds, compete with his crops for the available sunlight, air, and nutrients in the soil. However, it is only recently, with the exponential growth in the world's population and the resultant demands placed upon the world's food supply, that man has developed the technical ability to selectively retard or prevent the growth of undesired plant species growing with his crops. One of the first herbicides was 2,4-dichlorophenoxyacetic acid (2,4-D), which became available in 1944 for the control of broad-leaved weeds. Since then, a number of other classes of herbicides have appeared, some of which are more selective than 2,4-D, give control at much lower rates of application, are less toxic to mammals, longer lasting, easier to use, cheaper, and do not leave residues harmful to the environment. All of these characteristics are desirable features for a herbicide to possess.
Heterocyclic organic compounds are among the newer classes of herbicides. For example, the six-member s-triazine ring system is the central structural feature in a number of commercial herbicides, including 2-t-butylamino-4-ethylamino-6-methoxy-s-triazine [Martin and Worthing, "Pesticide Manual," 4th Ed., British Crop Protection Council, Worcester, England, 1974, p. 477], 2-sec-butylamino-4-ethylamino-6-methoxy-s-triazine [ibid., p. 449], 2-chloro-4-cyclopropylamino-6-isopropylamino-s-triazine [ibid., p. 146], 2-chloro-4-ethylamino-6-isopropylamino-s-triazine [ibid., p. 23], and 2-chloro-4-(1-cyano-1-methylethylamino)-6-ethylamino-s-triazine [ibid., p. 137].
The six member 1,3-diazine (pyrimidine) ring system is less common among the known herbicides, but some 4,6-disubstituted and 2,4,6-trisubstituted 5-nitropyrimidines display herbicidal activity [Ger. Offen. 2,520,381] as do certain 2,6-diamino-5-pyrimidinecarboxamides [U.S. Pat. No. 3,845,055].
It has now been discovered that 5-pyrimidinecarbonitriles, having amino substituents in the 2 and 6 positions and an alkoxy substituent in the 4 position, are extremely effective herbicides, which control the growth of a range of grassy and broad-leaved weeds while not affecting desirable crops such as corn and cotton growing therewith. One advantage of the 2,4,6-trisubstituted 5-pyrimidinecarbonitriles of this invention is that many of them are effective at very low rates of application.